Electric Circuits
35.1 The simplest circuit is a battery and light bulb connected between the terminals of the battery.
external image Lightbulb_bw.GIFhttp://www.enchantedlearning.com/lgifs/Lightbulb_bw.GIF

35.2 There must be a continues path for electricity to flow. The circuit will stop if there is an opening such as a switch. If the electricity flows through one device after another then it is a series circuit. If the deices form multiple paths that the electricity can take then it is a parallel circuit.
35.3
external image sci_dia_53.gifhttp://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_53.gif
Series Circuit:There is a single path through the circuit. If the current is interrupted at any pint then all current will stop. The total equivalent resistance of the circuit is the sum of the resistances of each element. The current is equal to the potential difference divided by the total resistance. The current in each element is equal to the total current in the circuit. The voltage drop across each element is equall to the current times the element's resistance. The total voltage across the circuit is equal to the sum of the voltage drops across each element.
35.4
external image sci_dia_55.gifhttp://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_55.gif
Parallel Circuit: Each element of a circuit connects the same two points so the voltage across each element is the same. The amount of acurrent in each element is inversely proportinoal to the resistance of the element. The total current in the circuit is equal to the sum of the currents through each element. As the number of parallel brances increases the total resistance of the decreases. The total resistance will be less than the resistance of any individual element.
35.5 There are commen symbols used...

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external image 00082.pngThe diagram left show a series circuit of a schematic diagram.

http://www.ibiblio.org/kuphaldt/electricCircuits/DC/00082.png


35.6 If two or more resistors are in a series the total resistance is the sum of the individual resistances. RT=R1+R2(+R3+...). If two or more sesistors are in a parallel then the inversse of the total resistance is the sum of the inverses of the individual resistances. 1/RT=1/R1+1/R2(+1/R3+...). If a circuit has a resistor in both series and parallel then you can apply the same process.
35.7 As more devices are added to a parallel circuit the total current will increase. Fuses and circuit breakers are used to limit the total current form increascing.